Дискретная математика . Индивидуальное задание.

#include <bits/stdc++.h>
using namespace std;

#define ll long long

const int MAXN = 20005;
vector<vector<int> > g(MAXN);
bool used[MAXN];
int timer, tin[MAXN], fup[MAXN];
vector<pair<int,int> >ans;

bool cmp(pair<int,int> a,pair<int,int>b)
{
    if(a.first < b.first) return true;
    if(a.first == b.first)
    {
        return a.second < b.second;
    }
    return false;
}

void dfs (int v, int p = -1)
{

    used[v] = true;
    tin[v] = fup[v] = timer++;
    for (size_t i=0; i<g[v].size(); ++i)
    {
        int to = g[v][i];
        if (to == p)  continue;
        if (used[to])
            fup[v] = min (fup[v], tin[to]);
        else
        {
            dfs (to, v);
            fup[v] = min (fup[v], fup[to]);
            if (fup[to] > tin[v])
                ans.push_back({min(v,to),max(v,to)});
        }
    }
}

void find_bridges(int n)
{
    timer = 0;
    for (int i=0; i<n; ++i)
        used[i] = false;
    for (int i=0; i<n; ++i)
        if (!used[i])
            dfs (i);
}

int main()
{
    ifstream filei("input.txt");
    ofstream fileo("output.txt");
    int N;
    filei>>N;
    int a;
    int Count =0;
    for(int i=0; i<N; ++i)
        for(int j=0; j<N; ++j)
        {
            filei>>a;
            if(a!=0 && a!=1)
            {
                fileo<<"Error";
                return 0;
            }
            if(a==1)
            {
                Count++;
                g[i].push_back(j);
                g[j].push_back(i);
            }
        }

    find_bridges(N);
    sort(ans.begin(),ans.end(),cmp);
    fileo<<ans.size()<<endl;
    for(pair<int,int> edge:ans)
    {
        fileo<<edge.first+1<<"-"<<edge.second+1<<" ";
    }
}